The invention relates to an apparatus for treating liquids and more specifically for mixing and/or aerating liquids, such as for example waste water.
Apparatuses of this type mainly comprise a power source such as a motor--which is mounted on a float and in which the power source drives an impeller device--such as a screw-shaped body--which is located at least partly beneath the surface of the liquid.
Floating mixers or aerators are generally known for treating waste water. Apparatuses of this kind are described in Belgian patents BE 884.216 and BE 893.687 in the Applicant's name.
One embodiment in which a single apparatus can be used as aerator and as mixer is described in Belgian patent 1.002.575. Mixing or aeration is carried out with this apparatus depending on the direction of rotation of the motor and thus of the screw. Thus, with one direction of rotation, the screw is made to axially pump the water upwards from below, after which the water is dispersed over the water surface at great speed. If the direction of rotation of the motor is reversed, the effect is obtained that the screw radially draws in the water from near the surface of the water and then pushes it axially downwards. In order to change over from aeration mode to mixing mode, the float is fitted with means for adjusting the immersion level of the apparatus.
During use of such apparatuses in liquids and also in contaminated water, it has been found that foam formation may take place at the surface of the liquid. This foam formation may lead to the motor or power source becoming defective if the foam builds up around it.